1. Field of the Invention
The present invention generally relates to a gasket placed between two mating surfaces to form a seal. More particularly, the present invention is directed to a metal gasket composed of a plurality of superimposed metal sheets, and a method of securing a plurality of metal sheets together to produce a metal gasket.
2. Description of the Related Art
Various types of metal gaskets are used throughout an automobile, particularly in an internal combustion engine. The joint between a cylinder block and a cylinder head must be sealed tight. It must hold the high pressure by combustion. The mating surfaces of the cylinder block and the cylinder head can not be machined smooth enough to provide the required seal. To this end, a head gasket is installed between the cylinder block and the cylinder head so as to prevent combustion leakage and loss of coolant or lubricant from the engine.
FIGS. 39 to 41 show part of a conventional metal gasket 1 shaped to fit a cylinder block (not shown), with all openings cut out. These openings include large openings 2 having a diameter equal to the diameter of each cylinder bore, a plurality of small openings 3 through which head bolts (not shown) are inserted to secure a cylinder head (not shown) to the cylinder block, and a plurality of openings 4 through which a coolant and a lubricant flow. As shown better in FIG. 41, the gasket 1 is composed of three thin sheets 5 to 7 made of metal and superimposed one above the other. Conventionally, grommets or eyelets are used to join the metal sheets 5 to 7 together. Specifically, a plurality of tongues or projections 8 extend horizontally from the outer periphery of each of the metal sheets. Each of the aligned projections 8 includes a through hole 8a to receive a grommet 9. The grommet 9 has a sleeve 9a, and two end flanges 9b extending radially outwardly from opposite ends of the sleeve 9a and adapted to clamp the inner peripheral edge of the projection 8 so as to secure the three metal sheets 5 to 7 together. Although the grommet 9 is durable and reliable, it is cumbersome to mount. The use of the grommet also increases the overall cost of the gasket.
As an alternative, spot welding could be used to easily secure a plurality of metal sheets. However, the spot welding can not be used in the case where coatings are applied to the surface of a metal gasket to provide a better seal.